Cooling system



NOV- 13, i945. c. D. MARsHYALLYErAL ,2,3895106 COOLING SYSTEM l FiledOct. 3, 1941 dwars/vm Q/Y/MLL.. Comeau. 0. f/Tr/LL INVENTORJ BY/ATTORNEY Patented Nov.. 13, f

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UNiraD srArss PATENT (orifice jzssam' 'Y ,Courtenay D. Marshall andCarrello. -ButtrilL Beaumont, Tex., asignen to Sooony-Vnonum OilCompany, Incorporated, New York, N. Y., a corporation of New YorkApplication embers, ieu, serial No. 413,428

I This invention has to do with the art of cooling and is particularlyconcerned with the operation of multiple pass direct refrigerationohillers While the invention herein disclosedl will be discussed in itsrelationship to the chilling oi' solvent-oil-wax mixtures and theapparatus used therein; this narrowing of the discussion is for v 1claim. (ci. iz-11o) y throughout such a direct expansion refrigerationY,

In order to understand thisinver'ition reference is now made to thedrawing attached hereto. This drawing-shows theprocessof the inventionand apparatus appropriate thereto in diagram convenience and forpurposes of exemplication,

and not by way of limitation.

In the chilling of solvent-oil-wax mixtures. hereinafter spoken of asoil, the oil is passed through a series of tubes, usually horizontallyarranged, in each of which tubes there is a helical rotating scraper toremove material, depositedl from the oil by cooling, from the internaltube wall. Each of these pipes or tubes is surrounded by a jacket and anoperating unit or chiller comprises several runs of such horizontaltubes..

For light cooling' duty. chilled brine is circulated through thejackets. For more severe duty, what is usually termed a direct expansionammonia separate ammonia expansion tank for each group with the rn thisdrawing, iackeiea shining tubes i, 2, a,

withdrawn from drum, I I by ,pump i2 and supplied under pressure to coldiluid header i3. from which pipe I4 'leadsto the jacket spaces ofchilling unit 5 and pipe I5 leads to the Jacket spaces oi chilling'unitI0. Leaving unit 5 under control of back pressure valve- Il and leavingunit-It` under control of back pressure valve` I1 the ycooling fluid iscollected incold fluid return llnekl and returned to expansion drum II.Vaporized refrigerant from expansion drum ii is drawn of! under thecontrol of back pressure valve Isfcompressed by compressor 20, `cooledin cooler 2l,-

and returned to expansion drum I l through compressed `iluid return line22A andppressure release valve 23. If found desirable, an additionalpressure releasevalve 2l may be Installedupon cold .iluid return line I8adjacent expansion vdrum II of horizontal tubes constituting a. singlechiller,

and fromthis tank the liquid ammonia is led by gravity into the annularjacket surrounding each ofv the several tubes. Even under very lowloadoperating conditions some oi' the liquid am mona further evaporat inthis annular space, and under high load conditions. as usuallyencountered,y this becomes' pronounced. As a result, the annular spaceis occupied notA by liquid but by a boiling liquid containing gasbubbles and in the upper portion by gas. This condition re duces theheat transfer capability of the unit.

Due to' this, such equipment has a very dennite for a purpose laterexplained.

The operation of this systemhas thei'ollowingl characteristics. Thetemperature of-the uid" cooling medium in expansion drum II can becontrolled by the inter-balance ot 4the rate ot pumping through' pumpYI2. the backpressure held upon the vapors. by bacio pressure valve I9, f

therate of vapor withdrawal so controlled, and the degree of pressuredrop through pressure re- Y leaseyalve 23. Having an ample supply ofcold fluid under pressure in the cold iluid header Il, ^an amountappropriate to th'e load being handled` l I, not only serves to controlthe amount so passed through the jackets oi.' this chiller, but alsoholds it under suilicient pressure to prevent its evaporation as heat iswithdrawn from the material being v it, il and 2t are adjusted manuallyfrom time to time, depending upon load conditions. Thus,

. if increased chillingis required, the pump l2 is speeded up, thuscausing increased cooling in both' of the units 5 and I0. If increasedcooling is required in only one of said unitsthe pump I2 is speeded andthe back-pressure valve associated with the unit not requiring increasedcooling is adjusted to raise the pressure therein. For example, ifincreased coolingis required only in the 'chilling unit 5, theback-pressure valve ll is adjusted to increase the pressure in thechilling unit I@ and the pump I2 is speeded. As a result, increasedcooling fluid passes through the chilling unit 5, while th'e flow ofcooling duid through the unit I8 remains substantially constant.

It is unnecessary to adjust the valves I 9 and 28. Valve 23 is apressure release valve which insures that the fluid back of the valveshall be main.

tained as a liquid while the fluid ahead of the valve coming into drumII i5 subjected to a reduced pressure which allows it to expand andevaporate. The back-pressure valve I9 is a differential pressure valvewhich insures that the pressure at the intake side of th'e compressor 20is normally lower than that in the expansion drum il, and also serves toprevent fluid from flowing from the compressor side oi the valve back tothe drum I I.

Automatic control could be devised to control the valves i6 and il andthe pump i2 depending upon the temperatures in the chilling units E andI@ and the relation of these temperatures to each other. For example, ifthe temperature in either chilling unit increases above a certainpredetermined maximum the pump I2 could be speecled. Alternatively, thespeed of th'e pump could be controlled by the maximum temperature ineither of the chilling units so that the higher the temperature ineither of said unitsl the greater the speed of the pump and the lowerthe temperature the lower the speed of the pump. Also, a control couldbe devised for the back-pressure valves IS and Il so that the lower thetemperature in either of said units, the higher the pressure should beadjusted for the valve controlling it. However, the automatic control ofth'ese valves and pumps is not a part of our invention and so need notbe described in detail. Formerly, under gravity distribution, anincrease in load of any slight proportion caused excessive vaporizationin the jacekt spaces, which cut down the heat transfer rate where vaporwas present, increased the load upon remaining liquid covered heattransfer surfaces, caused vapor formation there, and so compounded theevil and effectively prevented the handling of lheavier loadings Withthe present operation, increased loading merely calls for increased flowof cooling fluid, the increased flow f uid is heid `by back pressurevalve I6 under lcharged into the expansion drum II by the cold fluidreturn and' there is converted to latent heat of vaporization inrefrigerant vapor, to be removed with that vapor and withdrawn from thesystem by cooler 2|.

This system is, of course, applicable to any cooling system wherein arefrigerant medium is self cooled by partial vaporization and theremaining liquid circulated into indirect heat transfer relationsh'ipwith the materialto be cooled. While applicable to single cooling unitsit is most appropriate to systems where multiple cooling units operatein parallel from a single source of compressed refrigerant, giving tosuch systems a complete flexibility in the distribution of load amongthe several cooling units and permitting wide variations in the loadwhich may be assumed by any unit without disturbing the operation of theoth'er units. It does away with the provision of a separate expansiondrum for each unit which has formerly been the only way of approachingindependent adjustment of operation of an individual unit which is oneof several operating from single source of compressed refrigerant.

The difference in pressure between the expansion drum and the cold fluidheader, furnished by the cold uid circulating pump need not be muchgreater than that required to overcomev frictional resistance to liquidflow through the system. `when properly operated, this pump does notneed to furnish high pressure to overcome excessive vaporization in thechilling units. Even if so operated, however, the energy so expended canbe recovered, in large part. by regulated pressure release from the coldfluid return line into the expansion drum, the vaporization attendantupon said release offering opportunity for such recovery.

We claim: i

1. In the operation of a refrigeration system wherein liquid refrigerantis self-cooled by partial evaporation and the remaining liquid ls passedin heat exchange relationship with material to be cooled the methodwhich comprises conducting partial evaporation in a vessel iso-l latedfrom the material to be cooled, in which vessel a pool of cold liquidrefrigerant is main tained and from which vessel vapors are Withdrawn,to be compressed, liquefied, returned, and allowed to evaporate, andcirculating cold liquid refrigerant from said pool to the material to becooled and back to said pool while maintaining upon the liquid socirculated a pressure above that existing in the pool and sulcient topreventl substantial vaporization of the liquid refrigerant while it isbeing circulated from said pool to the material to be cooled and back tosulcient pressure to keep it liquid. and since increased liquid velocitygives higher h'eat transfer rate..the increased loading actuallyincreases the eiliciency of operation within reasonable limits.

The cooling Vuid discharged from the jackets of each chilling unit goesto the cold fluid return line, which acts as a collecting manifold incase a number of units are used. In some cases, under thesecircumstances. Athe use of a back pressure valve, as at 24, upon thecold fluid return line, may be useful4 in securing uniformity ofoperation in this pipe.. l

Heat removed from the chilled material is disfrigerant from said poolinto a manifold pipe at a pressure above that existing in said pool,

passing liquid refrigerant from said manifold in at least one stream inheat exchange relationship with material to be cooled and thence back tosaid pool, and maintaining upon saidstream,

while in said heat exchange relationship, a pressure sulciently elevatedabove that in said pool to prevent substantial evaporation vof theliquid refrigerant while in said stream.

v3. In the operation of a refrigeration system wherein liquidrefrigerant is self-cooled by partial evaporation and the remainingliquid is passed in heat exchange relationship with material to becooled the method which comprises conducting partial evaporation in avessel isolated rom the material tobe cooled, in which vessel a pool ofcold liquid refrigerant is maintained,land from which vessel vapors arewithdrawn, to be compressed, liqueed, returned and allowed toevaporatedeiiveringcold liquid rean expansion drum adapted to maintain apool ci cooled refrigerant, a -vapor circuit comprising a back-pressurevalve, a compressona cooler and a pressure release valve whereby vaporsmay be withdrawn from, compressed and liquefled, cooled and revaporizedin said expansion drum, a pump-for withdrawing liquid from said pool, aconduit whereby liquid from said pool may frigerant from said pool intoa manifold pipe at a pressure above Vthat existing in said pool, passingliquid refrigerant from said manifold in material to be cooled andreturned to said pooll and a back pressure valve in said conduit betweensaid 4material to be cooled and said pool.

6. In a refrigerating system whereina liquid refrigerant is self-cooledby partial evaporation and the remaining liquid is passed in heatexchange relationship with'materal to be cooled, lan expansion drumadapted to Vcontain a pool of `cooled refrigerant, a vapor circuitcomprising a a plurality of 'streams through cooling units wherein eachstream is in heat exchange relationship with material to be cooled,returning said streams to said pool, and maintaining upon the liquidrefrigerant while in said streams a pressure sufllciently elevated abovethat'- in said pool to prevent substantial vaporization of the i liquidrefrigerant while in said stream.

4. In a. refrigeration system wherein liquid reback-pressure valve, acompressor, a cooler and apressure release valve whereby vapors may be 1withdrawn from, compressed, cooled and revafrigerant is self-cooled. bypartial evaporation and the remaining liquid is passed in heat exchangerelationship with material to be cooled the-method which comprisesconducting partial evaporation in a vessel isolated from the material tobe vapors are withdrawn, to be compressed, liqueed, returned, and:allowed to evaporate, de-

livering cold liquid refrigerant from said pool into a manifold pipe ata pressure above that existing in said pool, passing liquid refrigerantfromI said manifold in a plurality of streams through cooling unitswhereineach stream is in heat exchange relationship with material toporized in said expansion drum, a pump for withdrawing liquid from saidpool, a manifold into which liquid is discharged' from said pump,conduits whereby separate streams of liquid may be led from saidmanifold, passed in heat exchange relation with the material to becooled, and returne to said pool, and in each conduit a back press evalve located between said material to so be cooled and said pool.

7. In a refrigerating system wherein a liquid refrigerant ,isself-cooled by partial evaporation and the remaining liquid is passedin. heat exchange relationship with material to be cooled.

35 an expansion drum adapted tocontaina pool oi cooled refrigerant, avapor circuitcomprising a back-pressure valve, a compressor, a coolerand a pressure release valve whereby vapors may be withdrawn from,compressed, cooled' and re- 40 vaporized in said expansion drum, a pumpfor be cooled, collecting the several streams together and returningthem to said pool, controlling the quantity of each stream in responseto the requirements ofthe material to be cooled, and

maintaining upon the liquid refrigerant in each stream a'pressuresufllciently elevated above that in said pool to prevent substantialvaporization of the liquid msaid stream.

` 5. In a refrigerating system wherein a liquid refrigerant isself-cooled by partial evaporation` andthe remainingliquidispusedinheatexchange relationship with material to be cooled,

, back-pressure valve located between the matewithdrawing liquid fromsaid pool, va manifold into which liquid is discharged from said pump,conduits whereby separate streams of liquid may be led from saidmanifold, and passed in heat relation with the material to be cooled, a,second manifold wherein said streams are re-oollected and returned tosaid pool, in each conduit a rial to be cooled and the re-collectionmanifold,

- and aback-pressure valve between said re-eollection manifold and saidpool.

COURTENAY D. MARSHALL.

CARROLL O. Bumm

